Rename the "flush space" to something more representative; suggest "flex space," "flexible space" or "expanding space."

This element was named in the narrow sense of allowing the last line of a justified paragraph to expand fully to the right margin. With the more obvious and accessible option of "full justification" this purpose of the space element is diminished, and it has use in other ways such as auto-spacing multiple words or phrases across a single line.

Renaming this feature, with no other changes, would make its purpose and availability more apparent to all users. (Even as an ACP/ACE and 20-year user, I did not realize InDesign had this equivalent of the "spring tab" found on other applications... the narrow naming and functional description kept me from realizing its true function.)